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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 



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Introduction to Electronics: The 

555 Timer Integrated Circuit 

(IC) 

Written By: KRA5H 



TOOLS: 

Snap Circuits Extreme 750 (1) 
available from RadioShack 
Snap Circuits Motion Detector (1) 
available from RadioShack 



PARTS: 

Base Grid (11"x 77") #6SCBG(1) 
Eight-Pin IC Socket #6SC?U8(1) 
• Whistle Chip #6SCWC(1) 
Variable Resistor #6SC RV (1) 
9V Holder & Switch (for SCP-03) # 6SC 
B5(2) 

Single Snap Conductor # 6SC 01 (4) 
Conductor with 2-snaps # 6SC 02 (7) 
Conductor with 3-snaps # 6SC 03 (2) 
Conductor with 4-snaps # 6SC 04 (3) 
555 Timer IC (1) 

TLC555/TLC555CP LinCMOS Timer (8- 
Pin DIP) available at radioshack.com 



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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 

0.02uF Capacitor # 6SC C1 (1) 



SUMMARY 

In this article, you will learn how to improve your collection of Snap Circuits blocks by 
adding a 555 Timer IC. You will learn the functions the pins on the 555 chip. You will learn 
that when the 555 is in astable mode, the output of pin 3 is a continuous stream of pulses 
called a square wave that can be heard on a piezoelectric speaker as a tone. Finally you will 
learn how to build an astable mode circuit for the 555. 

Snap Circuits is an educational toy that teaches electronics with solderless snap-together 
electronic components. Each component has the schematic symbol and a label printed on its 
plastic case that is color-coded for easy identification. They snap together with ordinary 
clothing snaps. The components also snap onto a 10 X 7 plastic base grid analogous to a 
solderless breadboard. 

All the kits include manuals printed in color with easy-to-follow diagrams to assemble the 
projects. The illustrations for each project look almost exactly like what the components will 
look like on the base grid when finished. Because the electronic symbol is printed on each 
electronic component, once the project is completed, it will look almost exactly like an 
electronic schematic. 

Currently there are no Snap Circuits sets that have the 555 Timer IC. So, you will need to 
purchase a 555 Timer IC from RadioShack. If you don't have the Snap Circuits Extreme SC- 
750 set you can purchase the Snap Circuits Eight-Pin IC Socket block from C&S Sales. 
Adding these two components to your set of Snap Circuits blocks will allow you to create 
dozens of circuits built around the 555 Timer IC. 



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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 



Step 1 — Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 

• The 555 Timer IC was introduced 
by a company called Signetics 
(later bought out by Philips) in 1972 
and was designed by Hans R. 
Camenzind in 1971. 

• The 555 chip has 25 transistors, 15 
resistors and 2 diodes in an 8 pin 
DIP (Dual In-line Package) and 
looks like a square bug with eight 
legs. 

• It has a notch at the top and Pin 1 
is in the top left corner. 

• Picture source 




Step 2 











© z ® © 

(?U8) B 

4 5 6 





• Insert the 555 timer chip into the 
Snap Circuits Eight-Pin IC Socket 
block (?U8). Make sure that the 
notch in the top of the 555 timer 
chip is aligned with the diagram of 
the chip pictured on the IC socket 
block. 



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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 
Step 3 



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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 

• Pin 1 is ground. It is connected to 
the negative side of your battery or 
power supply along with any other 
components in your circuit 
connected to ground. 

• Pin 2 is the Trigger pin. It will be 
connected to ground and thus 
switches on pins 3 and 7. 

• Pin 3 is the Output pin. In this 
circuit it outputs a square wave 
signal that can be heard on a 
speaker. 

• Pin 4 is the Reset pin. It is not 
used in this circuit. 

• Pin 5 is the Control pin. It is not 
used in this circuit. 

• Pin 6 is the Threshold pin. The 
capacitor that we will connect to 
the 555 will charge up and when it 
reaches about 2/3 Vcc (voltage 
from the battery), this is detected 
by the Threshold pin. This will end 
the timing interval and send Ov to 
the Output pin 3 (switch it off). 

• Pin 7 is the Discharge pin. It is also 
switched off by the Threshold pin 6. 
When switched off, it cuts the 
power to the capacitor causing it to 
discharge. Pin 7 also controls 
timing and is connected to the 50K 
ohm Variable Resistor RV. Moving 
the slider on RV changes the 
resistance thus changing the timing 
and the pitch heard on the speaker. 

• Pin 8 is connected to the positive 



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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 



side of your battery or power along 
with any other components in your 
circuit connected to positive. 



Step 4 




♦ Add the Snap Circuits blocks to the 
base grid as demonstrated in the 
picture. 



Step 5 




• Add the Snap Circuits blocks to the 
base grid as demonstrated in the 
picture. 



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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 
Step 6 



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Introduction to E 




r Integrated Circuit (IC) 

• Once you complete the circuit, 
switch on the 9 Volt Battery Holder 
(B5). You will hear a tone from the 
Whistle Chip. Move the slider on 
the Variable Resistor (RV) and you 
will hear the tone rise and lower in 
pitch depending on which way you 
move the slider. 

• The 555 chip is in "astable mode" 
which means that Pin 3 is sending 
a continuous stream of pulses 
called a square wave signal to the 
piezoelectric speaker (WC) that 
you hear as a tone. The square 
wave signal is caused by the 
charging and discharging of the 
capacitor. When you switch on the 
power: 

• Step 1 . The capacitor charges 
up. When the charge in the 
capacitor reaches 2/3 Voltage, 
this is detected by pin 6, the 
Threshold pin. 

• Step 2. The Threshold pin 6 
switches off the Output pin 3 and 
pin 7, the Discharge pin. 

• Step 3. When the Discharge pin 
7 is switched off this cuts the 
power to the capacitor which 
causes it to discharge. When the 
discharging capacitor reaches 
1/3 Vcc, this is detected by the 
Trigger pin 2. 

• Step 4. The Trigger pin 2 sends 
voltage from the battery to pin 3 



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Introduction to Electronics: The 555 Timer Integrated Circuit (IC) 



(the Output pin) and same 
voltage to pin 7 (the Discharge 
pin) which causes the capacitor 
to charge up (go back to step 1). 

• This process repeats creating the 
square wave signal and you hear 
that signal from the speaker as a 
tone. 

• When you move the slider on the 
Variable Resistor (RV) this 
changes the resistance of the 
circuit. Since the Variable resistor 
is connected to pin 7, changing the 
resistance controls the timing of 
how often the capacitor charges 
and discharges which changes the 
pitch you hear from the speaker. 



Step 7 



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(-) 5V 


5V 


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I eo aD J—- 



9V Holder & SW: 

5V - regulated 5V outputs 
(-) - power return to battery 
Snap for 9V battery 
ON/OFFswitch 



• To power the 555, you can use the 
Snap Circuits B5 block (it is also 
called a 9 volt Holder and Switch). 
The advantage to using this block 
is that you can connect a standard 
9 volt battery to the block and it will 
deliver a reliable 5 volts to the 555 
through the L7805 voltage regulator 
circuit (see circuit schematic). 

• The B5 also has two 5 volt outputs- 
-one to power the 555 circuit and 
one that you can use to power 
another device. 



st generated on 2012-10-31 07:51:24 AM. 



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